The present invention relates to the field of oil and gas drilling. More specifically the present invention relates to an apparatus and method for selecting or controlling, from the surface, the direction in which a wellbore proceeds.
A drill operator often wishes to deviate a wellbore or control its direction to a given point within a producing formation. This operation is known as directional drilling. One example of this is for a water injection well in an oil field which is generally positioned at the edges of the field and at a low point in that field (or formation).
In addition to controlling the required drilling direction, the formation through which a wellbore is drilled exerts a variable force on the drill string at all times. This along with the particular configuration of the drill can cause the drill bit to wander up, down, right or left. The industrial term given to this effect is xe2x80x9cbit-walkxe2x80x9d and many methods to control or re-direct xe2x80x9cbit-walkxe2x80x9d have been tried in the industry. The effect of bit walk in a vertical hole can be controlled, by varying the torque and weight on the bit while drilling a vertical hole. However, in a highly inclined or horizontal well, bit-walk becomes a major problem.
At present, in order to deviate a bole left or right, the driller can choose from a series of special downhole tools such as downhole motors, so-called xe2x80x9cbent subsxe2x80x9d and more recently a steerable motors.
A bent sub is a short tubular that has a slight bend to one side, is attached to the drill string, followed by a survey instrument, of which an MWD tool (Measurement While Drilling which passes wellbore directional information to the surface) is one generic type, followed by a downhole motor attached to the drill bit. The drill is lowered into the wellbore and rotated until the MWD tool indicates that the leading edge of the drill bit is facing in the desired direction. Weight is applied to the bit through drill collars and, by pumping drilling fluid through the drill string, the downhole motor rotates the bit.
U.S. Pat. No. 3,561,549 relates to a device which gives sufficient control to deviate and start an inclined hole from or control bit-walk in a vertical wellbore. The drilling tool has a non-rotating sleeve with a plurality of fins (or wedges) on one side is placed immediately below a downhole motor in turn attached to a bit.
U.S. Pat. No. 4,220,213 relates to a device which comprises a weighted mandrel. The tool is designed to take advantage of gravity because the heavy side of the mandrel will seek the low-side of the hole. The low side of the wellbore being the side furthest away from the vertical.
U.S. Pat. No. 4,638,873 relates to a tool which has a spring-loaded shoe and a weighted heavy side which can accommodate a gauge insert held in place by a retaining bolt.
U.S. Pat. No. 5,220,963 discloses an apparatus having an inner rotating mandrel housed in three non-rotating elements.
Thus, it is known how to correct a bit-walk in a wellbore. However, if changes in the forces that cause occur while drilling, all the prior art tools must be withdrawn in order to correct the direction of the wellbore. The absolute requirement for tool withdrawal means that a round trip must be performed. This results in a compromise of safety and a large expenditure of time and money.
The applicant""s own previous patent application WO 96/31679 and U.S. Pat. No. 5,979,570 partially addresses the problem of bit-walk in an inclined wellbore. The device described in this patent application and patent comprises eccentrically bored inner and outer sleeves. The outer sleeve being freely moveable so that it can seek the low side of the wellbore, the weighted side of the inner eccentric sleeve being capable of being positioned either on the right side or the left side of the weighted portion of the outer eccentric sleeve to correct in a binary manner for bit walk.
The applicant has now developed an improved downhole tool which can correct for bit walk in a highly inclined wellbore and which is capable of controlling both the inclination and the Azimuthal plane of the well bore.
In a first aspect, the present invention provides an apparatus for selectively controlling the direction of a well bore, the apparatus comprising:
a mandrel rotatable about a rotation axis; a direction controller means comprising at last two members spaced apart along said mandrel and configured to apply a force to said mandrel with a component perpendicular to the said rotation axis;
a housing having an eccentric longitudinal bore forming a weighted side and being configured to freely rotate under gravity; and
a driver for selectively varying the angle of the force relative to the weighted side of the housing about said rotation axis, the driver being capable of moving the two parts independently of one another.
The provision of a two part direction controller allows more control over the drilling direction in order to drill in a required direction and to compensate for bit-walk. Further, the provision of a two part direction controller allows a null or a zero force to be applied to the mandrel by precessing the direction controller about the mandrel.
The two parts of the direction controller can be configured in a number of different ways. Preferably, the two parts are located on different sides of the central plane. A particularly preferable arrangement is achieved when both of the two parts are capable of applying a independent force to the mandrel. For example, the two parts may be located on either side of the central plane of the housing. For example, both parts may comprise eccentric sleeves.
In an alternative configuration, only one part is capable of applying a radial force to the mandrel, the other part only being capable of applying a symmetric force about the mandrel. For example, one part may be an eccentric sleeve and the other may be a concentric sleeve. If the arrangement is envisaged where a concentric sleeve is located on one side of the central plane and an eccentric sleeve is located on the other, then it is possible to form a so-called xe2x80x9cpoint the bitxe2x80x9d arrangement. The eccentric sleeve may be located either above or below the central plane of the housing. Two eccentric sleeves oriented at 180xc2x0 to each other about the mandrel can also achieve this effect.
References have been made to the at least one part being eccentrically bored. However, it should be noted that the same effect can be achieved with a sleeve which is spatially symmetric about the rotation axis, but which has a denser material or a weight located at one side of the sleeve.
Further there is no requirement for the direction controller to be a sleeve. A cam or even a linear actuator could be used to the same effect as an eccentric sleeve.
The driver is configured to move the two parts of the direction control means independent of one another. This is applicable regardless of the nature of the direction controller for example if the direction control means comprises a sleeve, cam, linear actuator or another component which can achieve the same result.
Where the direction controller comprises a linear actuator, the actuator may be mounted such that that can move about the circumference of said mandrel to apply a force to the mandrel at the required position. Preferably, a plurality of linear actuators are placed around the circumference of the mandrel. More preferably, at least three actuators are used at equal angles in a plane about said mandrel. The three actuators being capable of applying a force to the mandrel in any direction in a plane about its axis. Therefore, in a second aspect, the present invention provides an apparatus for selectively controlling the direction of a wellbore, the apparatus comprising: a mandrel which is rotatable about a rotation axis;
a direction controller comprising at least one linear actuator configured to apply a force to said mandrel;
a housing having an eccentric longitudinal bore and being configured to freely rotate under gravity; and a drive means for selectively varying the angle of the force relative to the weighted side of the housing about said rotation axis.
Preferably, the driver in accordance with either the first or the second aspects of the present invention is configured to change the direction of the force within a tolerance of at most 10xc2x0, more preferably at most 5xc2x0, even more preferably at most 1xc2x0.
A possible configuration of the driver and the direction controller can be achieved by drive wheel and track arrangement.
The track and drive wheel preferably comprise a plurality of interengaging teeth to effect movement therebetween. Such an arrangement is commonly referred to as a pinion and drive wheel arrangement. This arrangement is particularly preferable as, when stationary, the drive wheel locks against the track serving to secure the inner sleeve in position relative to the housing. The track and drive wheel arrangement could also be provided by a drive wheel with a circumference which has a high coefficient of friction with the said track.
The said drive wheel may be located on a part of the direction controller and the housing may be provided with a track on its internal surface, such that movement of the drive wheel causes movement of the said part of the direction controller with respect to the housing. Alternatively, the drive wheel may be located in the outer housing and a part of the direction controller may be provided with a track such that movement of the drive wheel affects relative movement between the said part of the direction controller and the housing. This arrangement is preferable as it allows a power source to drive the drive wheel to be located within the housing.
The above drive means have been described with relation to the movement of a single part of the direction controller. However, a single drive wheel could be used to move the two parts of the direction control means. Two such drive means may be used to drive the two parts of the direction controller respectively.
The driver may comprise a hydraulic or electric motor or the like. Further, drive means may be battery powered or powered by the rotation of the rotating mandrel.
In operation, the driver is required to move the direction of the force with respect to the outer housing. Typically, some means are required to instruct the driver to move the position of the direction of application of the force on the mandrel.
Therefore, the apparatus preferably further comprises logic means for determining when the direction of the force applied by the direction controller should be moved. The logic means may be located in the downhole assembly, or they may be located at the surface with means for communicating with the downhole assembly. If the logic means are located within the downhole assembly they may be configured to send and/or receive information from the surface in order to determine when the direction of the force should be moved.
If the logic means are located at the downhole assembly and are configured to receive information from the surface, preferably information is sent to the logic means using one of the parameters which are readily available during drilling. For example, the weight on the drill bit and pump cycling.
The logic means may comprise a sensor for sensing a wellbore fluid pulses and decoding said pulses to determine when the direction of the force should be changed. A series of fluid pulses can be sent down said drill string. The drill string pulses can be used to encode data to send to the downhole assembly.
The fluid pressure could also be used to determine the position of the force of the direction controller. For example, fluid passageways could be provided which extend generally radially through said mandrel, said direction controller and said housing such that, when said direction controller, which may for example, be a sleeve, cam etc., is in a first position, said series of drilling fluid passageways align with each other so as to allow drilling fluid to flow readily from said interior of the said mandrel to said exterior of said housing accompanied by a relatively low pressure drop, and when said sleeve is not in the fist position, said drilling fluid passageways are in misalignment so as to restrict drilling fluid flow from said interior of said mandrel to said exterior of said housing accompanied by relatively high pressure drop. This allows the position of the direction control means to be determined.
In a preferred arrangement, the above is achieved by the provision of a bit-jet and orifice combination positioned within said generally radial passageway in said mandrel adjacent said direction control means.
Further, the logic means may comprise a detector for detecting the rotating of the drill string. The drill string rotation could be detected by using magnetic fields for example in the manner described in GB 2 356 207. The logic means may be configured to detect the frequency rotation of the drill string. This allows a magnitude of a scalar parameter such as an angle through which to move the force applied by the direction control means. The logic means may be configured to determine a time period between rotation and non-rotation of the drill string wherein said time period determines when the angle of said force should be changed with respect to the weighted side of said housing or the radial position of the housing.
The logic means and the driver may be stored within the housing. Alternatively, the logic means may be located within a tubular housing connected to at least one of the mandrels, direction controller and housing. The apparatus may further comprise an energy source for supplying power to the driver and/or logic means.
Preferably, the rotating mandrel is terminated at both ends in the appropriate standard tool joint used in the drilling industry for ready attachment to subs, the bit, other downhole tools, or drill pipe.
The rotating mandrel is used to transfer the rotary motion of the drill pipe to the drill bit and acts as continuation conduit of the drill pipe for all drilling fluids passing down the drill pipe and onto the drill bit.
The above description has primarily considered sending information from the surface to the downhole assembly in order to change the position of the force on the mandrel. However, during drilling, the downhole assembly is actually located within the wellbore, therefore the downhole assembly itself is a far better position to determine data concerning the strata then any surface based analysis equipment.
Therefore, preferably, the downhole assembly is provided with a sensor for sensing geological information about the formation being drilled.
Therefore, in a third aspect, the present invention provides an apparatus for selectively controlling the direction of a well bore comprising a mandrel rotatable about a rotation axis; a direction control means comprising configured to apply a force to said mandrel with a component perpendicular to the said rotation axis; a housing having an eccentric longitudinal bore forming a weighted side and being configured to freely rotate under gravity; a drive means for selectively varying the angle of the direction of force about said rotation axis; and sensing means for sensing information about the formation which is being drilled.
The sensing means preferably comprises a sensor and analysing means for analysing data collected by the sensor. If the analysis is performed by the downhole assembly, then there is no time wasted in sending the data to the surface. Another stage further would be to allow the tool to control itself on the basis of the data sensed by its sensors.
In a fourth aspect, the present invention provides an apparatus for drilling a well bore, the apparatus comprising a drilling member configured to drill in a predetermined drilling direction; direction control means for controlling the drilling direction of said drilling member; a sensor for determining at least a characteristic of the strata being drilled; wherein said direction control means determines the drilling direction based on the data collected by said sensor.
Preferably, the sensor is configured to detect gamma rays.
The apparatus may further comprise a plurality of stabiliser shoes. These stabiliser shoes may be circumferentially offset by a predetermined amount in relation to the weight of the housing. More preferably, the apparatus comprises two stabiliser shoes. The stabiliser shoes which may be blades, wedges etc. extend radially outward and laterally along the circumference on either side of the outer eccentric sleeve or outer housing.